Shifts in Riparian Plant Life Forms Following Flow Regulation

María D Bejarano,Alvaro Sordo-Ward,Xiaolei Su,Judith Sarneel

doi:10.3390/f11050518

María D Bejarano, Alvaro Sordo-Ward + Show 2 more

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https://doi.org/10.3390/f11050518

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Abstract

Flow regulation affects bordering riparian plant communities worldwide, but how different plant life forms are affected by river regulation still needs further research. In northern Sweden, we selected 10 rivers ranging from free-flowing to low, moderately, and highly regulated ones. In 94 reaches across those rivers, we evaluated the relative abundance of woody and herbaceous (i.e., graminoids and forbs) life forms, their species richness, and their relative presence. We also explored which, and to what extent, hydrological variables drove species assembly within each life form. The relative abundance and species richness of each life form decreased across river categories with increasing levels of regulation. This was particularly apparent in herbaceous life forms, and the most drastic decreases were observed in all life forms in moderately or highly regulated reaches. Additionally, when river regulation increased, the relative presence of many species from all life forms decreased. Unlike woody species, only a few new herbaceous species appeared in regulated reaches. A canonical correspondence analyses (CCA) revealed that a wide range of hydrological variables explained the occurrence of woody species, while fewer variables explained variation in the graminoid and forb life forms. We conclude that flow regulation and its intensity result into clear shifts in the relative abundance of different life forms, as well as in changes of within-group species richness and composition. Consequently, the modification of certain flow attributes in flow regulation schemes, as well as the intensity of these modifications, may alter the ratio between herbaceous and woody species, ultimately impacting the functions and benefits derived from each life form.

Highlights

IntroductionSince studies on many species at once are relatively scarce or restricted to smaller spatial scales, many questions about community responses are still unanswered
It is obvious that changed flow regimes affect plant growth, performance, and distributions [1,2].since studies on many species at once are relatively scarce or restricted to smaller spatial scales, many questions about community responses are still unanswered
Characteristic riparian forbs, graminoids, shrubs, and trees are arranged as clear belts at different elevations, parallel along the channel because each life form is thought to have a different resistance to the hydrological forces of the spring flood [26]

Summary

Introduction

Since studies on many species at once are relatively scarce or restricted to smaller spatial scales, many questions about community responses are still unanswered. This is unfortunate, as general frameworks (as opposed to species-specific or site-specific frameworks) are essential to develop flow management guidelines for regional or national water management plans. To overcome the difficulties of working at a species level, classification into functional groups has been advocated and used in other ecological theories [3]. Despite the growing number of studies using functional groups, they remain somewhat controversial because they depend on which traits have been considered, especially when classification is limited by the information that is available in trait databases [4]

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